Marine Exhaust System With Catalyst

ABSTRACT

A marine engine exhaust system is provided that utilizes a single catalyst housing through which exhaust gases from multiple heads of an exhaust system flow. A first conduit directs a first exhaust gas from a first engine head or exhaust manifold to the catalyst, and a second conduit directs a second exhaust gas from a second engine head or exhaust manifold to the catalyst. The first and second conduits may be separate or may merge prior to the catalyst. The catalyst includes a housing and at least one substrate to convert the first and second exhaust gases into processed exhaust gas. A third conduit directs the processed exhaust gas away from the catalyst. At least one pre-sensor may be located upstream of the catalyst housing, and at least one post-sensor may be located downstream of the catalyst housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to provisional applicationhaving U.S. Patent Application Ser. No. 62/129,225, filed on Mar. 6,2015, the contents of which are incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to a marine engine exhaust system thatincludes a catalyst for reducing emissions of the exhaust system. Moreparticularly, the present application includes a marine engine exhaustsystem that may include a single catalyst housing having at least onesubstrate that receives and processes exhaust from multiple heads of amarine engine.

BACKGROUND

Marine engines used to power watercraft, such as a boat, are susceptibleto being damaged through introduction of water. Water injection canoccur in a marine engine in several different manners. Although foursuch manners will be discussed it is to be understood that other typesare possible. The first mechanism is through wave action. Here, a surgeof water enters the exhaust and proceeds into the engine. The surge ofwater is produced from an external source such as the wake of a passingboat, inclement weather or turning of the watercraft. Water intrusionmay also occur when a boat is put in unusual attitudes, for example asport fishing boat backing up in heavy seas in which water is forcedinto the exhaust track in sufficient volume to enter the engine.

The second way in which water can be introduced into the marine engineis through by-products of the combustion process. As the gasoline/airfuel mixture undergoes combustion during the operation of the engine, achemical reaction takes place that may produce moisture within theengine components, which may negatively affect engine performance.

A third way of introducing water into the marine engine is by way ofcondensation. In general, condensation may occur in the system due tothe temperature differential of a hot engine and ambient air, and cancause engine malfunction. Marine engines must be cooled, such as withwater jacketing, to keep the engines from overheating, since they mustbe safely designed in order to be enclosed in a watercraft. This coolingcreates a lower temperature than land based engines. Condensation mayoccur through dissimilar cooling rates of various components, which mayoccur during cooling or subsequent to shutting down the engine.Temperature differences between daytime and nighttime may also causecondensation to form in the engine exhaust system. Further, condensationmay also result from having too low of an operating temperature of theexhaust system.

The fourth way through which water may be introduced into a marineengine is through reversion. Reversion occurs when the marine engine isidling and, due to camshaft timing overlap, the cooling water from theexhaust manifold/elbow actually migrates or “walks” backward in theexhaust track to the engine. Reversion is the backwards flow of exhaustgases during the time period in which both intake and exhaust valves aresimultaneously open, and primarily occurs when the engine runs at idlespeed or slightly above idle speed.

Water injected into a marine engine typically damages components, suchas exhaust valves, which prevents the cylinder with the damaged exhaustvalve from correctly sealing. This damaged cylinder then causes water tobe pulled into the engine through the corroded exhaust valve. This wateris redistributed to the rest of the engine and causes its ultimatefailure. The control of water injection is a primary objective ofwatercraft and engine manufacturers and is especially challengingconsidering the environment in which the watercraft is deployed.

Design of marine engine exhaust systems is further complicated by theneed to reduce emissions from marine engines as may be required bygovernment regulations. Current marine engine designs typically employ apair of catalysts that remove or reduce certain impurities or pollutantsfrom the exhaust gas streams emitted from either side of an inboardengine that has two cylinder heads. The engine could include two, four,six, eight, ten cylinders and these cylinders are typically divided sothat half are on one side of the engine, and the other half on the otherside of the engine. A standard design may include, for example, fourrunners associated with the individual exhaust ports on each side of theengine that includes a total of eight cylinders. Each side has an enginehead, which may have an exhaust manifold that receives the output fromthe four runners per side, and output from the exhaust manifold on eachside is in the form of a single common exhaust outlet on each side ofthe manifold.

The catalysts in marine engine exhaust systems are typically locateddownstream from the exhaust outlets on each engine head or exhaustmanifold, such that each exhaust manifold from each engine head has itsown catalyst. For instance, one catalyst is located downstream from theright side exhaust manifold outlet, and the other catalyst is locateddownstream from the left side exhaust manifold outlet. The catalystscould be behind the engine, on top of the engine, on the right or leftsides of the engine, or at any other location relative to the engine.Water that enters the marine engine exhaust system will also interferewith the proper functioning of the left and right side catalysts andassociated sensors because the catalysts and sensors cannot operatecorrectly if they are wet. Water introduced into the catalysts willcause their eventual failure. Since the catalysts are located downstreamfrom the engine and the exhaust manifolds, they are generally closer tothe introduction point of water into the system, thus making the overallsystem more susceptible to failure.

The use of two catalysts in existing marine exhaust systems requiresthat two catalyst monitoring systems be employed. The first catalystwill require a first oxygen sensor be located before, or upstream of thefirst catalyst to measure the exhaust gas before entering the firstcatalyst, and a second oxygen sensor to be located after, or downstreamof the first catalyst to acquire data about the exhaust gas exiting thefirst catalyst. The second catalyst will likewise require its own pre-and post-oxygen sensors to measure properties of the exhaust gas bothentering and exiting the second catalyst, and thus a second catalystmonitoring system may also be needed.

Single catalyst exhaust systems are employed in automotive engines, butthese automotive exhaust designs are not readily applicable to marineengines. The manufacture and/or marinization of engines for marine usein watercraft require unique considerations that are not relevant to theautomotive industry. For example, inboard marine engines and exhaustsystems are encased within the hull of the boat during use, so spatiallimitations and overheating issues are primary concerns for marineexhaust system design. Automotive exhaust systems, on the other hand,are open to the air underneath the automobile, and so do not have thesame heat concerns. Moreover, automotive exhaust systems are not locatedin immediate proximity to the engine, but rather extend under the bodyof the automobile. Marine exhaust systems, on the other hand, must becontained within the same limited space as the engine and transmission,and therefore packaging and interference with other components becomes acritical concern. Finally, marine engines and exhaust systems areintended for use on the water, and so water infiltration is a primaryconcern in the marine engine field. Automobiles, conversely, aredesigned for land-based use where water hazards are less extensive. Forthese and many other reasons, marine and automotive engines and exhaustsystems are not interchangeable.

Although current systems are capable of reducing emissions in marineengine exhaust systems, there remains room for variation and improvementwithin the art.

SUMMARY

The present invention is directed to a marine engine exhaust system fora dual-head or multi-head engine utilizing a single catalyst forprocessing all of the exhaust gas generated during combustion.Specifically, the present exhaust system includes a first conduit influid communication with exhaust gases exiting from a first engine head,and a second conduit in fluid communication with exhaust gases exitingfrom a second engine head. In at least one embodiment, the exhaustsystem includes a first exhaust manifold at the first engine head, and asecond exhaust manifold at the second engine head. The exhaust manifoldscollect exhaust gases from the respective engine heads, and may connectto the first and second conduits, respectively.

A catalyst is also in fluid communication with the first and secondexhaust gases, which are directed from the engine heads to the catalystby the first and second conduits. In some embodiments, the conduits maycombine to form a merged conduit before joining with the catalyst. Inother embodiments, the first and second conduits each join the catalyst.The conduits may connect to the catalyst at any surface, such as thetop, bottom, or sides of the catalyst.

The catalyst has a housing and at least one substrate positioned thereinin contacting engagement with the exhaust gases so as to convert theexhaust gases as they pass therethrough for emissions purposes. Thecatalyst may include one substrate or multiple substrates, but allsubstrates are located within the same housing.

The system further includes a third conduit in fluid communication withat least one processed gas exiting from the catalyst. Such processed gasis the result of the catalytic conversion reaction performed by thesubstrate(s) as the exhaust gases pass therethrough. The third conduitconveys the processed gas away from the engine for expulsion from thewatercraft. In at least one embodiment, the system may include a thirdand fourth conduits in fluid communication with the processed gas(es).The third conduit, and fourth conduit in appropriate embodiments, mayconnect to the catalyst at any surface, such as the top, bottom, orsides of the catalyst, and in at least one embodiment are locatedopposite of the first and second or merged conduit.

In some embodiments, the present exhaust system includes at least onepre-sensor located in monitoring engagement of the first and secondexhaust gases, and may preferably be located upstream of the catalyst.The exhaust system may also include at least one post-sensor located inmonitoring engagement of the processed exhaust gases, and may preferablybe located downstream of the catalyst. The pre-sensor(s) andpost-sensor(s) monitor the performance of the catalyst. Because thepresent invention includes only one catalyst housing, it is possible tohave only one pre-sensor and one post-sensor, thereby providing a moreefficient monitoring system.

The present exhaust system also contemplates the use of a water-cooledjacketing system to surround and cool the exhaust manifolds, conduitsand catalyst. In such embodiments, the third conduit includes a coolingwater introduction point at which water from the cooling system ispermitted to mix with the processed exhaust gases. Preferably, thiscooling water introduction system is located at a terminal end of thethird (and fourth) conduits, and permits mixing with the cooling waterjust prior to expulsion from the watercraft. This positioning reducesthe risk of water infiltration into the exhaust system and engine.

These and other features and advantages of the present invention willbecome clearer when the drawings and detailed description are taken intoconsideration.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended Figs. in which:

FIG. 1 is a perspective view of one example of a marine engine exhaustsystem showing a pair of conduits entering the catalyst.

FIG. 2 is a perspective view of another example of a marine engineexhaust system showing a pair of conduits merging before entering thecatalyst.

FIG. 3 is a perspective view of an example of a marine engine exhaustsystem showing the conduits entering the catalyst from the bottom andexiting from the top of the catalyst.

FIG. 4 is a schematic diagram of a marine engine exhaust system with apair of conduits entering the bottom of the catalyst.

FIG. 5 is a schematic diagram of a marine engine exhaust system with apair of conduits that merge exhaust gases before entering the bottom ofthe catalyst.

FIG. 6 is a schematic diagram of a marine engine exhaust system with apair of conduits that enter the side of the catalyst.

FIG. 7 is schematic diagram of a marine engine exhaust system with apair of conduits that enter the top of the catalyst.

FIG. 8 is a schematic diagram of a marine engine exhaust system with apair of conduits that merge exhaust gases before entering the top of thecatalyst.

FIG. 9 is a schematic diagram of a marine engine exhaust system with apair of conduits that enter the side of the catalyst and output of thecatalyst out of the bottom of the catalyst.

FIG. 10 is a schematic diagram of a marine engine exhaust system with apair of conduits entering the side of the catalyst and a pair ofconduits exiting the bottom of the catalyst.

FIG. 11 is a schematic diagram of a marine engine exhaust system with apair of conduits entering the top of the catalyst and a pair of outletconduits exiting the sides of the catalyst.

FIG. 12 is a cross-sectional schematic diagram of one example of acatalyst showing a single substrate.

FIG. 13 is a cross-sectional schematic diagram of another example of acatalyst showing multiple circular substrates within the housing.

FIG. 14 is a cross-sectional schematic diagram of another example of acatalyst showing multiple rectangular substrates within the housing.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, and notmeant as a limitation of the invention. For example, featuresillustrated or described as part of one embodiment can be used withanother embodiment to yield still a third embodiment. It is intendedthat the present invention include these and other modifications andvariations.

It is to be understood that the ranges mentioned herein include allranges located within the prescribed range. As such, all rangesmentioned herein include all sub-ranges included in the mentionedranges. For instance, a range from 100-200 also includes ranges from110-150, 170-190, and 153-162. Further, all limits mentioned hereininclude all other limits included in the mentioned limits. For instance,a limit of up to 7 also includes a limit of up to 5, up to 3, and up to4.5.

The present invention provides for marine engine exhaust system 10 thatincludes a catalyst 12 and limits or prevents water from damaging theengine 14 and the catalyst 12. The system 10 includes a single catalyst12 that processes exhaust gases from multiple different engine heads orexhaust manifolds. The catalyst 12 includes a housing 70 and at leastone substrate 72, and the exhaust gases 50, 52 from the first and secondmanifolds 16, 18 are both be directed through and treated by thesubstrate(s) 72 of the single catalyst 12 to remove pollutantstherefrom. The resulting processed exhaust gas 80 can be subsequentlymerged with cooling water 46 upon exiting the exhaust system. Thevarious components of the exhaust system 10 and conduits 20, 22, 24 and26 can be water jacketed for cooling purposes of the system 10.

Accordingly, the present invention provides a more efficient marineexhaust system than previously known. The single catalyst housing 70through which all the exhaust gases 50, 52 flow provides a single pointfor emissions processing. This translates to a reduction in the numberof pre-sensors and post-sensors needed to monitor the exhaust gas andcatalyst operation. The electrical wiring and harnesses are thereforealso simplified since fewer sensors and other components are needed. Italso simplifies and improves engine calibration and efficiencymonitoring, since only one catalyst must be monitored.

Moreover, by cutting the number of catalysts in half, the presentexhaust system reduces the chance for exhaust leaks by 50% and reducesthe chance for coolant leaks by 50%, thus providing a more safe exhaustsystem. Having a single catalyst that processes all exhaust gases 50, 52means that the exhaust manifolds are freed of individual catalysts. Incurrent marine engine exhaust systems, each exhaust manifold typicallyhas its own dedicated catalyst which is attached directly to the exhaustmanifold. The attachment of the catalyst to the exhaust manifold createsa moment arm, or cantilever effect, which induces bolt stress on theexhaust manifold, leading to breakage over time. The current inventioneliminates this mechanical stress by uncoupling the catalyst from theexhaust manifold and using only a single catalyst for all exhaust gases,regardless from which exhaust manifold they emanate.

The present marine engine exhaust system 10 may be used with any type ofmarine watercraft engine. For example, the present exhaust system 10 canbe used with inboard engines, which are enclosed within the hull of aboat. Other arrangements are possible in which the marine engine exhaustsystem 10 is used in connection with an outboard engine, which islocated external to the hull. The system 10 can also be used with acombination inboard/outboard engine, sometimes known as a stern drive.

For example, in FIG. 1, one embodiment of the exhaust system 10 of thepresent invention is shown in in conjunction with a marine engine 14.The exhaust system 10 of the present invention may be used with any sizeor power of engine. For instance, the exhaust system 10 can be utilizedwith engines having any number of cylinders or pistons, such as 4cylinder, 6 cylinder, V-6 or V-8 engines. The cylinders may bepositioned in any configuration throughout the engine, but mosttypically are present as equal numbers of cylinders on each side of theengine, which may be arranged vertically or at a slight angle or pitchwithin the engine block. The engine size can be any displacement,including but not limited to 5.1 liter, 5.7 liter, 6.0 liter, 6.2 liter,8.1 liter or any other sized engine suitable for marine watercraft,including those intended for towing. The present exhaust system 10 isintended for use with combustion engines, such as gasoline orpetrol-based engines, although under certain circumstances dieselengines may be used.

The upper portions of the cylinders on one side of an engine arereferred to collectively as an engine head. FIG. 1 shows one embodimentof the system 10 from a perspective illustrating one side of the engine14, showing a first engine head 86. A second engine head 88 on theopposite side of the engine 14 is also indicated. Exhaust gases from theindividual runners of individual exhaust ports at the first engine head86 are referred to here as a first exhaust gas 50. Similarly, on theother side of the engine, exhaust gases from the individual runners ofthe individual exhaust ports at the second engine head 88 form thesecond exhaust gas 52.

In at least one embodiment, as in the Figures, the exhaust system 10includes a first exhaust manifold 16 that channels and combines thefirst exhaust gas 50 from the first engine head 86. Similarly, a secondexhaust manifold 18 channels and combines the second exhaust gases 52from the second engine head 88. Any type of exhaust manifold may beemployed in the present exhaust system 10, as indicated by theirschematic representation in FIGS. 1-3. For instance, the exhaustmanifolds 16, 18 may be log manifolds, or may be pyramidal, linear,curved, “banana”, or tubular shaped, or any other configuration asenables the combination of exhaust gases from cylinders of the engine.Further, the exhaust manifolds 16, 18 may be made of any suitablematerial, including but not limited to metals such as stainless steel,ceramic, or other materials, and may be made by casting from a mold,welding, layering, plating, spray-coating, or other methods ofmanufacture typical for exhaust manifolds.

The exhaust system 10 includes a first conduit 20 in fluid flowcommunication with a first exhaust gas 50 exiting from a first enginehead 86 such that the first exhaust gas 50 enters the first conduit 20as it exits from the first engine head 86. Similarly, the system 10 alsoincludes a second conduit 22 in fluid flow communication with a secondexhaust gas 52 exiting from the second engine head 88. In someembodiments, the exhaust gases 50, 52 go directly from the cylinderexhaust port at the engine heads 86, 88 into the first or secondconduits 20, 22, respectively. In other embodiments, as shown in FIGS.1-3, the exhaust gases 50, 52 generated at the engine heads 86, 88 arecollected in exhaust manifolds 16, 18 before being directed into thefirst or second conduits 20, 22, respectively.

“Conduit” as used herein means an elongate enclosed structure having twoopposite open ends, defining a hollow interior extending through thelength between the opposite open ends, so as to receive, convey anddeliver fluids from one location to another over a distance. Theconduits 20, 22 are preferably tubes, such as pipes, formed of a solidwall defining a hollow interior through which the fluids, such asexhaust gases 50, 52 are conveyed. They may be any length. The conduits20, 22 may have any cross-sectional shape, such as circular, oval,square, rectangular, or irregular, although circular or oval may bepreferable in some embodiments. The conduits 20, 22 may also besymmetrical or asymmetrical in cross-section. The conduits 20, 22 mayhave any diameter appropriate for the volume of exhaust gas 50, 52 to betransferred or conveyed therethrough. For example, the diameter of theconduit 20, 22 is large enough to allow movement of the volume ofexhaust gases 50, 52 generated by the engine at a flow rate sufficientto permit clearance of the gases 50, 52 from the engine heads 86, 88 andcatalytic conversion of the exhaust gases 50, 52, as described ingreater detail below. Accordingly, the conduits 20, 22 may attach insealing engagement to the engine heads 86, 88 or exhaust manifolds 16,18 and may be aligned so that the hollow interior of the conduits 20, 22meet up with the opening(s) of the engine heads 86, 88 or exhaustmanifolds 16,18 for transfer of exhaust gases 50, 52.

The conduits 20, 22 may be made of metals, such as stainless steel oraluminum, or any suitable material for connecting to the engine heads86, 88 or exhaust manifolds 16, 18 in sealing engagement andtransferring the hot exhaust gases therein. Further, in the embodimentsof FIGS. 1-3, the conduits 20, 22 may be made of a rigid material.

The conduits 20, 22 may include one or more bends 38, 40 which changethe direction of the conduit 20, 22 for fluid flow. A bend may thereforechange the shape or configuration of the conduit without changing thediameter or cross-section of the conduit. For instance, a bend mayredirect the conduit in any direction within a 360° rotation from thepoint at which the bend begins, and may provide redirection of anoverall acute or obtuse angle. Accordingly, bends 38, 40 may be used toroute the conduits 20, 22 from the engine heads 86, 88 or exhaustmanifolds 16, 18, around the engine 14 and toward the catalyst 12, as isbest illustrated in FIGS. 1-3. Any number of bends 38, 40 iscontemplated as may be appropriate to achieve a desired route for theconduits 20, 22 around the other components of the engine 14 or exhaustsystem 10, which may vary depending on the particular engine used.Therefore, any configuration of exhaust system 10, conduits 20, 22 andbends 38, 40 is contemplated herein.

Moreover, the bends 38, 40 may constitute a sharp or gradual change indirection, although a gradual change is preferable. For example, evenwhen a bend 38, 40 redirects the conduit 20, 22 by 90°, such as in FIG.1, the change may be sufficiently gradual that the conduit wall remainscurved and not angular, and there is not a point or edge defined by thebend 38, 40. In some embodiments, however, points or edges may be formedby the bend 38, 40.

In some embodiments, the conduits 20, 22 and bends 38, 40, respectively,are formed of a single or unitary piece, as may be made by casting,forming or hammering of material. In other embodiments, the bends 38, 40may be joints combining different sections of conduit 20, 22 together topermit usage of rigid materials and still direct the flow of exhaustgases 50, 52 as needed. In still other embodiments, the conduits 20, 22are made of flexible or semi-flexible material, such as thermo-resistantplastics or polymers, or pliable metals, which permit changes indirection without the use of bends 38, 40 or joints. Such materials maybe bent or hammered in a desired configuration, after which they mayremain in their formed shape.

The first and second conduits 20 and 22 may be oriented in a variety ofmanners with respect to one another. They may be symmetrical withrespect to one another such that the conduits 20, 22 are symmetricalabout a midline of the engine 14. The conduits 20 and 22 may turn towardthe opposite side of the engine 14 so that they directly face oneanother, or so that they face one another on an angle, which may alsoextend upwards or downwards. The conduits 20 and 22 need not besymmetrical with one another in other embodiments and can be shapeddifferently, have different cross-sectional sizes, geometries and/ordifferent lengths.

Continuing with FIGS. 1-3, the conduits 20, 22 direct the exhaust gases50, 52 from each engine head 86, 88 or exhaust manifold 16, 18 to thecatalyst 12 for processing. Accordingly, the catalyst 12 is in fluidflow communication with both of the first and second exhaust gases 50,52. The catalyst 12 has a single housing 70 containing at least onesubstrate 72 therein. Exhaust gases 50, 52 from both of the conduits 20,22 enter the housing 70 of a single catalyst 12. The housing 70 issufficiently large to accommodate the substrate(s) 72 contained therein,in whatever configuration they may be. For instance, since there is onlya single catalyst 12 and must be able to process the exhaust gasescoming from two manifolds, in one embodiment the catalyst 12 is twicethe size of catalysts currently used on each exhaust manifold in marineengines. However, in other embodiments, such as with increasedefficiency in catalytic substrate material and/or configurations, lesssize may be needed to accomplish the same catalytic conversion process.Therefore, in such embodiments, the catalyst 12, though but a singlecatalyst, may be the same size as current catalysts, or may even besmaller or more compact. The housing 70, accordingly, is sized toaccommodate the substrate(s) 72 that are needed for catalyticconversion. The housing 70 may be made of any suitable material, suchas, but not limited to, metals such as stainless steel, aluminum ortitanium, ceramic, or other materials.

As the exhaust gases 50, 52 travel through the catalyst 12, they mixwith one another and are treated by the catalyst 12, specifically thesubstrate(s) 72 therein, to convert them for emissions purposes and toremove pollutants. The substrate(s) 72 is disposed or positioned withinthe housing 70 of the catalyst 12 in contacting communication with theexhaust gases 50, 52 as they pass through the catalyst 12. As theexhaust gases 50, 52 come into contact with the substrate(s) 72, thesubstrate(s) 72 act on them to perform a chemical reaction, such asoxidation or reduction reactions, or other chemical reactions,converting them into different chemical compounds that are less toxic tothe environment. Pollutants may also be removed. These are commonlyknown processes that occur in catalysts and catalytic converters alreadywell known. For instance, substrate(s) 72 may include any commonly knowncatalytic substrate materials, including precious metals such asplatinum, palladium, rhodium. These materials may also be heat tolerantat temperatures generated in the engines and exhaust systems. Forexample, the catalyst 12 and substrate(s) 72 therein can withstandtemperatures in the range of 400°-1600° Fahrenheit. In a preferredembodiment, the temperatures are optimal at 1200°-1600° F., and mostpreferably at 1400° F. It should be understood that the temperatureincreases with more pollutants, and so the catalyst 12 may withstandeven the higher range of temperatures.

Moreover, the substrate(s) 72 may be present in any configuration orarrangement within the housing 70 as permits contacting engagement withthe exhaust gases 50, 52 and chemical conversion thereof. For instance,the substrate(s) 72 may have a honeycomb structure or pattern as isknown for catalytic substrates, such as in monoliths. The cell densityof the honeycomb structure may be any as allows for a sufficient airflow rate and contacting engagement with the exhaust gases to performcatalytic conversion. For example, an air to fuel ratio of 14.7:1 isconsidered optimal for catalytic conversion performance. In at least oneembodiment, the substrate(s) 72 comprise a cell density of 400 holes persquare inch. In another embodiment, the substrate(s) 72 has a celldensity of thousands of holes per square inch. The number and size ofsubstrate(s) 72 included in the catalyst 12, and the size and number ofcells or holes therein, will depend on the size and demand of theengine, and the volume and rate of exhaust gases 50, 52 generated.Generally speaking, the larger the engine, or the more cylinders in theengine, the larger and/or more substrate(s) 72 will be used in thecatalyst 12, and will have larger sized holes for air flow through thesubstrate(s) 72. Moreover, while a honeycomb pattern is common, otherpatterns are also contemplated. For instance, rod structures may also beused. Multiple substrate(s) 72 or materials therein may be disposed inlayers with relation to each other, which may be offset from one anotherto increase surface area for contacting engagement with exhaust gases50, 52. These are just a few non-limiting examples for illustrativepurposes.

FIGS. 12-14 depict various schematic embodiments of the housing 70 andsubstrate(s) 72 configurations therein of the catalyst 12 of the presentexhaust system. For instance, in the embodiment of FIG. 12, the housing70 includes a single substrate 72 which fills up substantially theentire interior of the housing 70. This configuration may maximizecontact between the substrate 72 and exhaust gases 50, 52 for processingand chemical conversion. In the embodiment of FIG. 13, the housing 70may include two substrates 72, such as when catalysts from two exhaustmanifolds are combined into a single catalyst 12. They may include afirst substrate 73 and a second substrate 74, which may vary from oneanother in composition, configuration, cell density, or othercharacteristic. In other embodiments, first and second substrates 73, 74may be the same as each other in all relevant characteristics exceptposition within the housing 70. In the embodiment of FIG. 14, threesubstrates 72 are present and aligned in such a way as to maximizecontacting engagement with the exhaust gases 50, 52 passing through. Itshould be appreciated from these examples that any number of substrates72 may be present in the catalyst 12, so long as they are all present inthe same single housing 70. Moreover, the substrates 72 may comprise anyshape or dimension as permits chemical conversion of the exhaust gases50, 52, such as circular, rod-shaped, rectangular, square, or othershapes. Similarly, the housing 70 may be any shape or dimension asaccommodates the desired substrate(s) 72 in the desired configuration.

As noted above, as the exhaust gases 50, 52 pass through the catalyst 12and make contact with the substrate(s) 72 therein, they undergo chemicalprocesses that convert them to other compounds. The gases that have beenconverted are now processed exhaust gases 80. In a preferred embodiment,the catalyst 12 converts the first and second exhaust gases 50, 52 intoat least one processed exhaust gas 80, which may include a plurality ofgases. These processed exhaust gases 80 may be consistent with theemissions requirements for combustion engines in a particular state orcountry.

Returning to FIGS. 1-3, the marine exhaust engine system 10 alsoincludes a third conduit 24 in fluid communication with the processedgas(es) 80 exiting from the catalyst 12. For example, the third conduit24 connects to the catalyst housing 70 in fluid flow communication withthe processed gas(es) 80 to route them away from the catalyst 12 and outof the exhaust system 10. Accordingly, the third conduit 24 may beattached in sealing engagement to the catalyst housing 70. As with thefirst and second conduits 20, 22, the third conduit 24 can be rigid andmade of a metal such as aluminum, or may be a flexible member in yetother embodiments. The third conduit 24 may be made of the same materialas the first and second conduits 20, 22 described above, and may furtherinclude one or more bends or other device to chance the direction of thethird conduit 24 for routing purposes. In a preferred embodiment, thethird conduit 24 routes the processed gases 80 to the back of the boator watercraft for exiting the boat, although the third conduit 24 mayroute the processed gases 80 in any direction.

Marine engines require additional considerations unique to watercraft,such as protecting the engine and other components from waterinfiltration and heat concerns from compact space limitations andconformations, often known as packaging. Accordingly, the exhaustmanifolds 16, 18, catalyst 12 and the various conduits 20, 22, 23, 24and 26 described herein may be surrounded by water jackets through whichcooling water 46 runs to act as a heat sink and keep the temperature ofthe components from climbing too high and overheating. This water jacketsystem is preferably carried throughout the various components of theexhaust system 10. The water-cooled jacketing system may be aclosed-loop system in which at least a portion of the cooling water 46is recirculated through cooling system. In other embodiments, thewater-cooled jacketing system is open-ended, such that cooling watertraveling through the system exits the cooling system at the sameterminal end of the exhaust system 10. Cooling water 46 may be freshwater or salt water, and may be supplied from a reservoir or pumpeddirectly from the body of water in which the watercraft is at leastpartially submerged.

Cooling water 46 may exit from the water jacketing system and may bemixed with the processed exhaust gases 80 at a cooling waterintroduction point 36. Once the cooling water 46 is added, a combinedprocessed exhaust gas and cooling water stream 48 is created and issubsequently transferred out of the marine engine exhaust system 10 intothe body of water in which the boat 44 is located. For the catalyst 12to function properly, no cooling water 46 should be present within theexhaust gas 50, 52 entering the catalyst 12. The chemical reactionsnecessary for removing contaminants from the gas stream will not work,or will not function as well, if cooling water 46 is mixed with theexhaust gas affected by the catalyst for contaminant removal. As such,cooling water 46 may be missing from the gas stream at all pointsupstream from point 36 all the way back through to the engine 14.

Therefore, in at least one embodiment, the cooling water introductionpoint 36 is located as far downstream (at the end of the exhaust system10) as possible from the catalyst 12, such as at the terminal end of thethird conduit 24, to provide maximum distance between the catalyst 12and limit water infiltration into the exhaust system 10. In anotherembodiment, the third conduit 24 includes at least one bend, such asdescribed above in relation to the first and second conduits 20, 22, tocreate a more convoluted route for the processed gas 80 before thecooling water introduction point 36. In such an embodiment, the bends inthe third conduit 24 may function as obstacles to inhibit waterinfiltration from the cooling water introduction point 36. The thirdconduit 24 may include any number of bends between the catalyst 12 andthe cooling water introduction point 36 to achieve this purpose. Inanother embodiment, the cooling water 46 exits the water jacketingsystem at the cooling water introduction point 36 as a mist, therebyreducing the amount of water that could potentially back up into theexhaust system 10.

FIGS. 4-11 illustrate various configurations for the third conduit 24and cooling water introduction point 36.

In at least one embodiment, the first and second conduits 20, 22 aredirected toward each other from opposite sides of the engine and connectto the catalyst 12 at the top. For instance, the first and secondconduits 20, 22 connect individually to the catalyst 12, as in theembodiments of FIGS. 1 and 7. In these embodiments, the first exhaustgas 50 coming from the first engine head 86 or exhaust manifold 16 andthe second exhaust gas 52 coming from the second engine head 88 orexhaust manifold 18 are kept separate and do not co-mingle until theyare within the catalyst 12. In other embodiments, as in FIGS. 2 and 8,the first and second conduits 20, 22 merge upstream of the catalyst 12,forming a merged conduit 23. In the merged conduit 23, the first andsecond exhaust gases 50, 52 co-mingle to form a combined exhaust gas 54.The merged conduit 23 connects to the catalyst 12, and the combinedexhaust gas 54 enters the catalyst 12.

In these embodiments, the first and second exhaust gases 50, 52 enterthe catalyst 12 from the top 60. In other embodiments, the exhaust gases50, 52, 54 enter the catalyst 12 from the bottom. For instance, FIGS. 3and 4 show embodiments in which the first conduit 20 and second conduit22 connect to the catalyst 12 at the bottom separately. In FIG. 5, thefirst and second conduits 20, 22 may merge upstream of the catalyst 12to form a merged conduit 23 which subsequently connects to the catalyst12 from the bottom.

As can be appreciated from the Figures, the merged conduit 23 may be aseparate component or a part of either the first or second conduits 20,22, and may be at any angle with relation to either the first or secondconduits 20, 22. For instance, the merged conduit 23 may be a separatesection of conduit from the first and second conduits 20, 22, as in FIG.5. It may be positioned at a 90° angle in relation to the first andsecond conduits 20, 22, as in FIG. 5, or may be at an angle less than orgreater than 90° to the conduits 20, 22. In other embodiments, themerged conduit 23 may be a portion of the first and/or second conduits20, 22, which may even be shared in common, as in FIG. 2.

Further, the third conduit 24 which directs processed exhaust gas 80away from the catalyst 12 may connect to the top, bottom, or sides ofthe catalyst 12. In at least one embodiment, the third conduit 24connects to the catalyst 12 opposite of the first and second conduits20, 22 or merged conduit 23. For instance, the third conduit 24 mayconnect to the bottom 62 of the catalyst 12, as in FIGS. 1, 2 and 7-9.In some embodiments, the third conduit 24 connects opposite of the firstand second conduits 20, 22, as in FIGS. 1, 2, 7 and 8. In otherembodiments, the third conduit 24 is not opposite of the first andsecond conduits 20, 22, such as in FIG. 9 where the first and secondconduits 20, 22 enter the catalyst 12 from opposite sides of thecatalyst 12, and the third conduit 24 connects to the bottom 62 of thecatalyst 12. In other embodiments, as in FIGS. 3 and 4-6, the thirdconduit 24 connects to the top 60 of the catalyst 12. It shouldtherefore be appreciated that the first and second conduits 20, 22 ormerged conduit 23 directing the exhaust gases 50, 52, 54 into thecatalyst 12 and the third conduit 24 directing the processed exhaustgases 80 out of the catalyst 12 may connect to any side or surface ofthe catalyst 12 as would permit flow of the gases through the catalyst12.

While it may be preferable to have a single conduit conveying theprocessed gases 80 away from the catalyst and out of the boat, so as tosimplify manufacturing, packaging and housing considerations, there maybe more than one such conduit in certain embodiments. For example, asseen in FIGS. 10 and 11, the exhaust system 10 may include not only athird conduit 24 in fluid communication with a processed gas exitingfrom the catalyst 12, but also a fourth conduit 26 in fluidcommunication with a processed gas exiting from the catalyst 12. In someembodiments, both the third and fourth conduits 24, 26 receive anddirect the same processed exhaust gas 80 away from the catalyst 12. Inother embodiments, the third conduit 24 may receive a first processedexhaust gas 82 from the catalyst 12, and the fourth conduit 26 receivesa second processed exhaust gas 84 from the catalyst 12. In suchembodiments, the first and second processed exhaust gases 82, 84 maycomprise the same composition of gases, but one may be from a firstsubstrate 73 within the catalyst 12 and the other may be from a secondsubstrate 74 within the catalyst 12. Examples of this are illustrated inFIGS. 10 and 11. In other embodiments, the first and second processedgases 82, 84 may comprise difference compositions.

FIG. 13 shows an example of the inside of a catalyst 12 having a firstand second substrate 73, 74 that may be used to separately processexhaust gases 50, 52, and optionally may direct the resulting processedexhaust gases 82, 84 into a third and fourth conduit 24, 26. In thisexample, the first substrate 73 may be in contacting engagement with afirst exhaust gas 50 which comes from a first engine head 86 or manifold16, and results in a first processed exhaust gas 82. A second substrate74 may be in contacting engagement with a second exhaust gas 52 comingfrom a second engine head 88 or exhaust manifold 18, resulting in asecond processed exhaust gas 84.

The present exhaust system 10 also includes at least one pre-sensor 28in contacting engagement with the first and second exhaust gases 50, 52,and at least one post-sensor 32 in contacting engagement with theprocessed exhaust gas(es) 80 to measure the performance of the catalyst12. For instance, as seen in FIG. 4, the first exhaust gas 50 travelsthrough the first conduit 20 and a first pre-sensor 28 acquires dataabout the first exhaust gas 50 before or as it enters the catalyst 12.The second conduit 22 can also include a pre-sensor 28 that acquiresdata about the second exhaust gas 52 before it enters the catalyst 12.The pre-sensor(s) 28 can sense any type of property or propertiesassociated with the exhaust gas streams 50 and 52, such as, but notlimited to, carbon dioxide, carbon monoxide, nitrogen oxides,temperature, pressure, and air flow rate. In a preferred embodiment, thepre-sensor 28 is an oxygen sensor.

The first pre-sensor 28 can be located at the conduits 20, 22 at anypoint along the length of the conduit 20, 22. For example, in oneembodiment, the pre-sensor 28 may be located at the point where theconduit 20, 22 meets the engine head 86, 88 or exhaust manifold 16, 18.In another embodiment, the pre-sensor 28 may be located in the wall ofthe conduit 20, 22 just downstream of where the conduit 20, 22 meets theengine head 86, 88 or exhaust manifold 16, 18. In still otherembodiments, the pre-sensor 28 may be located at the point where theconduit 20, 22 meets the catalyst housing 70. The pre-sensor 28 may alsobe located at the conduit 20, 22 just prior to the point of joining withthe catalyst housing 70. In other embodiments, the pre-sensor 28 may belocated upstream of a bend(s) 38, 40 in the conduit 20, 22. Thepre-sensor 28 may also be located downstream of a bend(s) 38, 40 in theconduit 20, 22. In still other embodiments, the pre-sensor 28 may belocated in the catalyst housing 70 at or near the point where theconduit 20, 22 joins the housing 70. In some embodiments, there aremultiple pre-sensors 28 along the conduit 20, 22, which may be disposedanywhere along the length of the conduit 20, 22 and/or the catalysthousing 70.

In other embodiments, as in FIG. 2, the pre-sensor 28 may be located inthe merged conduit 23, so that the exhaust gases 54 are monitored beforeentering the catalyst 12. In still other embodiments, as in FIGS. 1 and3, the pre-sensor may be located in the catalyst 12 itself, such as at apoint near the entry of the first and second exhaust gases 50, 52, so asto measure the gases prior to catalytic processing.

The catalyst 12 receives the first and second exhaust gas streams 50, 52and functions to remove pollutants therefrom as described above. Thecatalyst 12 can be any type of catalyst used with engine exhaustsystems. The catalyst 12 may work best if the first and second exhaustgas streams 50, 52 are both hot and dry. The exhaust gases 50, 52 arelikewise mixed within the catalyst 12 along with being treated by thecatalyst 12 to remove pollutants. This mixing may occur while thecatalyst 12 is removing contaminants, or may be done before the catalyst12 removes contaminants or even after removal of the contaminants, orany combination of the aforementioned sequences. As such, the catalyst12 may function to both mix the exhaust gases 50, 52 in addition totreating the exhaust gases 50, 52 for contaminant removal. The singlecatalyst 12 may be included such that a second catalyst 12 is notnecessary as all of the exhaust gas 50, 52 is treated by the singlecatalyst 12. As such, all of the exhaust of the engine 14 may flowthrough this single catalyst 12, even though this exhaust may come fromopposite sides of the engine 14.

At least one post-sensor 32 is provided after the catalytic processingto measure certain properties of the processed exhaust gas(es) 80, sothe performance of the catalyst 12 can be monitored and the efficiencydetermined. As with the pre-sensor(s) 28, the post-sensor(s) 32 maymeasure and/or monitor properties be such as, but not limited to, oxygenlevels, carbon dioxide levels, carbon monoxide levels, nitrogen oxideslevels, temperature, pressure, and air flow rate. The post-sensor(s) 32also be used to determine if the catalyst 12 has stopped working, or ifthere is a leak in the system.

The post-sensor 32 may be located anywhere downstream of the catalyst12. In some examples, as in FIGS. 1-4 and 7, the post-sensor 32 islocated at the third conduit 24 and measures one or more properties ofthe processed exhaust gas 80 flowing through the third conduit 24. Inother embodiments, such as in FIGS. 10 and 11, the third and fourthconduits 24, 26 each include a post-sensor 32 to monitor the propertiesof the processed exhaust gases 82, 84 flowing through each,respectively. The post-sensor 32 may be located anywhere along theconduits 24, 26, such as at or just after their connection point withthe catalyst 70, or anywhere along their length between the catalyst 12and the cooling water introduction point 36 so that monitoring is notimpeded by potential water infiltration. In at least one preferredembodiment, the post-sensor 32 is located within the conduit(s) 24, 26as far away from the cooling water introduction point 36 as is possible.In embodiments in which the third or fourth conduits 24, 26 include atleast one bend, the post-sensor 32 may be located before or after anyone of the bends along the conduit 24, 26. In still other embodiments,the post-sensor 32 may be located in the catalyst 12, but at a pointthat is downstream of the catalyst conversion processes occurring in thesubstrate(s) 72, such as at the point of exit of the catalyst 12.

The various arrangements of the marine engine exhaust system 10discussed herein are all similar in that they utilize a single catalyst12 for cleaning all of the exhaust gases 50, 52 from engine heads 86, 88or exhaust manifolds 16, 18 generated by the combustion process in theengine 14. For example, the arrangement of FIG. 5 is different than thatof FIG. 4 in that the first conduit 20 and the second conduit 22 mergewith one another such that the first exhaust gas 50 and the secondexhaust gas 52 also merge with one another prior to the catalyst 12. Theconduits 20, 22 are in communication with one another at a merge pointfrom which the merged conduit 23 extends. The pre-sensor 28 is locatedin the merged conduit 23 and the combined first and second exhaust gas54 travels through the merged conduit 23 and into the catalyst 12through the bottom of the catalyst 12. The exhaust gas stream 54 doesnot need to be mixed in the catalyst 12 since it is already mixed, butthe catalyst 12 still treats the exhaust gas stream 54. The thirdconduit 24 exits through the top surface 60 of the catalyst 12 and theprocessed exhaust gas 80 is measured at a post sensor 32 in the thirdconduit 24.

The arrangement of FIG. 6 is the same as that previously discussed withrespect to the system 10 of FIG. 4 except that the first and secondconduits 20 and 22 enter the catalyst 12 through the side surface 58 ofthe catalyst 12 instead of through the bottom surface 62. The catalyst12 may be cylindrical in shape such that it has a cylindrical shapedouter surface 58, and the conduits 20, 22 can enter through oppositesides of the outer surface 58. In other embodiments, the catalyst 12 canbe variously shaped and need not be cylindrical. Likewise, instead ofexiting the top surface 60, the third conduit 24 having the processedexhaust gas 80 may exit through the bottom surface 62 or the sidesurface 58 in other exemplary embodiments.

FIG. 7 shows another embodiment of the system 10 in which a pair of gasstreams 50 and 52 enter the catalyst 12 and are mixed therein andtreated. The system 10 of FIG. 7 is similar to that of FIG. 4 exceptthat the first and second conduits 20, 22 terminate at the upper surface60 of the catalyst 12 instead of the lower surface 62. After the exhaustgas streams 50 and 52 mix and are treated in the catalyst 12, they exitthe catalyst 12 through the bottom surface 62. The processed exhaustgases 80 are measured by the post-sensor 32 in the third conduit 24, andthe processed exhaust gases 80 are eventually mixed with cooling water46 at point 36. The system 10 employs three sensors 28, 32 that aremeasured by a catalyst 12 monitoring system of the system 10. Thesensors 28, 32 provide information as to how the catalyst 12 isfunctioning and as to the emissions being removed from the combinedgases 54.

FIG. 8 shows an alternate arrangement of the system 10 in which thefirst and second conduits 20, 22 merge with one another to form a mergedconduit 23 before the catalyst 12. The first and second gases 50, 52merge into the combined stream 54 in the merged conduit 23, and aremeasured by the pre-sensor 28. There is some amount of conduit 23 thatextends from the merge point of the first and second conduits 20, 22 tothe top surface 60. The pre-sensor 28 may be located at merged conduit23. With this arrangement, only one pre-sensor 28 may be needed sincethe gases 50, 52 merge before entering the catalyst 12.

The third conduit 24 extends from the bottom surface 62, and theprocessed exhaust gases 80 are measured by the post-sensor 32 afterbeing treated by the catalyst 12. In other arrangements, the thirdconduit 24 can exit from the side surface 58 or the top surface 60 ofthe catalyst 12. The processed exhaust gases 80 are transferred throughthe third conduit 24 to such a point 36 in which cooling water 46 ismixed therewith to form the combined gas and cooling water stream 48. Inother arrangements, the processed exhaust gases 80 may not mix withcooling water 46 in the third conduit 24 or at any point in the system10.

The arrangement in FIG. 8 employs only two sensors 28, 32 and does notneed to have three sensors in the catalyst 12 monitoring of the system10. Also, as only a single catalyst 12 is used, a second catalyst withits associated weight, size, positioning, and catalyst monitoring systemis not needed.

FIG. 9 shows another arrangement of the marine engine exhaust system 10that is similar to that previously discussed with respect to the systemof FIG. 7. However, the system 10 in FIG. 9 is different in that thefirst and second conduits 20, 22 enter the side surface 58 of thecatalyst 12 instead of the top surface 60. The third conduit 24 exitsthe bottom surface 62, and sensors 28, 32 are employed along with thesingle catalyst 12.

The marine engine exhaust system 10 may be configured so that only asingle exhaust outlet, for example the third conduit 24, leaves theengine 14 and includes the combined exhaust gas and cooling water stream48, as in FIGS. 1-9. However, in other embodiments, twin exhaustgas/cooling water conduit streams can be provided in the design. Forexample, FIG. 10 is an alternative exemplary embodiment of the system 10in which the first and second exhaust gases 50, 52 enter the catalyst 12through the side surface 58 and mix therein and are treated therein forthe removal of pollutants. A pair of outlets composed of a third conduit24 and a fourth conduit 26 exit the bottom surface 62, and combinedexhaust gases 54 flow out of the catalyst 12 and into both of theconduits 24 and 26. The third conduit 24 is equipped with a firstpost-sensor 32 to measure the processed exhaust gases 82 in the thirdconduit 24. The fourth conduit 26 has a second post-sensor 34 thatmeasures a property or properties of the processed exhaust gases 84 inthe fourth conduit 26. Each of the conduits 24, 26 has a water mergepoint 36 in which cooling water 46 is merged with the processed exhaustgases 82, 84 to form the combined cooling water and exhaust gas streams48.

The pair of exhaust conduits 24, 26 allow for the provision of a dualexhaust arrangement of the system 10 with the use of but a singlecatalyst 12. There are two pre-sensors 28 and two post-sensors 32present in the system 10 for the measurement of the gases and propercontrol of the emission reduction. Although shown as exiting the bottomsurface 62, the various conduits 24, 26 can exit on any of the surfaces58, 60 and 62 in accordance with other arrangements.

FIG. 11 shows another alternative exemplary embodiment of the system 10that is similar to the system 10 of FIG. 10 in which the conduits 20 and22 enter the catalyst 12 through the top surface 60. Also, the third andfourth conduits extend from the side surface 58 of the catalyst 12instead of the bottom surface 62. As previously mentioned, the system 10includes various arrangements in which the various conduits 20, 22, 24and 26 can engage the catalyst 12 at any combination or one of the sides58, 60 and 62, and it is to be understood that the examples specificallyillustrated herein are only exemplary and that others are possible.

The exhaust gases 50 and 52 are mixed with one another in the catalyst12 in certain embodiments, and there is only one catalyst 12. The system10 may utilize a single catalyst monitoring system, since only a singlecatalyst 12 is employed. A single catalyst 12 and monitoring system maydecrease the size of the system 10 and give more space for othercomponents of the boat. Fewer components would be required and thus asavings on cooling hoses and materials would result. Also, as certainembodiments may require reduced sensors 28, 32, the wiring harness ofthe system 10 may be simplified. Engine 14 calibration may be improvedbecause combined exhaust from each engine head 86, 88 or exhaustmanifold 16, 18 allows the catalyst 12 to run more consistenttemperature and pressure gradients due to the steady flow of exhaustgases 50, 52. The combined exhaust gases in some arrangements allow foronly a pair of sensors 28 and 32 to be required. The combined exhaustarrangement allows the catalyst 12 to maintain light off temperatureeven at engine 14 idle conditions via the use of a closed loop coolingsystem. However, open loop cooling systems are used in otherarrangements. Also, a single exhaust design may allow the boat to bemore easily serviced and affords greater flexibility in boat design.

Additional information associated with portions of the marine engineexhaust system 10 such as water jacketing, conduit arrangements,sensors, catalyst monitoring, and the prevention of water through thesystem 10 and into the engine 14 may be provided as described in U.S.Pat. No. 6,644,024 to Powers et al; U.S. Pat. No. 7,803,026 to McKinney;and U.S. Pat. No. 3,206,836 to Schlussler the entire contents of whichare incorporated by reference herein in their entireties for allpurposes. Still further, the catalyst and catalyst monitoring system andother components associated with the catalyst may be provided asdescribed in U.S. Pat. No. 7,314,044 to Westerbeke, the entire contentsof which are incorporated by reference herein in their entirety for allpurposes.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

What is claimed is:
 1. A marine engine exhaust system, comprising: afirst conduit in fluid communication with a first exhaust gas exitingfrom a first engine head; a second conduit in fluid communication with asecond exhaust gas exiting from a second engine head; a catalyst influid communication with both said first and second exhaust gases havinga housing and at least one substrate positioned within said housing incontacting engagement with said first and second exhaust gases toconvert said first and second exhaust gases into at least one processedexhaust gas; and a third conduit in fluid communication with said atleast one processed exhaust gas exiting from said catalyst.
 2. Themarine engine exhaust system as recited in claim 1, further comprising afirst exhaust manifold interposed in fluid communication between saidfirst engine head and said first conduit, and a second exhaust manifoldinterposed in fluid communication between said second engine head andsaid second conduit.
 3. The marine engine exhaust system as recited inclaim 1, wherein said catalyst includes a first substrate in contactingengagement of said first exhaust gas to produce a first processedexhaust gas, and a second substrate in contacting engagement of saidsecond exhaust gas to produce a second processed exhaust gas.
 4. Themarine engine exhaust system as recited in claim 3, wherein each of saidfirst and second conduits is in fluid communication with said catalysthousing.
 5. The marine engine exhaust system as recited in claim 3,wherein said third conduit is in fluid communication with said firstprocessed gas exiting from said catalyst, and further comprising afourth conduit in fluid communication with said second processed exhaustgas exiting from said catalyst.
 6. The marine engine exhaust system asrecited in claim 1, wherein said first and second conduits join to forma merged conduit upstream of said catalyst, and wherein said mergedconduit is in fluid communication between said first and second conduitsand said catalyst housing.
 7. The marine engine exhaust system asrecited in claim 1, wherein each of said first and second conduits arein fluid communication with said catalyst housing.
 8. The marine engineexhaust system as recited in claim 1, further comprising at least onepre-sensor in contacting engagement with said first and second exhaustgases.
 9. The marine engine exhaust system as recited in claim 8,wherein said catalyst includes said at least one pre-sensor.
 10. Themarine engine exhaust system as recited in claim 8, wherein at least oneof said first and second conduits includes said at least one pre-sensor.11. The marine engine exhaust system as recited in claim 8, wherein saidfirst and second conduits join to form a merged conduit upstream of saidcatalyst, and wherein said merged conduit includes said at least onepre-sensor.
 12. The marine engine exhaust system as recited in claim 1,further comprising at least one post-sensor in contacting engagementwith said at least one processed exhaust gas.
 13. The marine engineexhaust system as recited in claim 12, wherein said catalyst includessaid at least one post-sensor.
 14. The marine engine exhaust system asrecited in claim 12, wherein said third conduit includes said at leastone post-sensor.
 15. The marine engine exhaust system as recited inclaim 1, wherein said first and second engine heads are located onopposite sides of an engine.
 16. A marine engine exhaust systemconsisting essentially of: a first conduit in fluid communication with afirst exhaust gas exiting from a first engine manifold; a second conduitin fluid communication with a second exhaust gas exiting from a secondengine manifold; a catalyst in fluid communication with both said firstand second exhaust gases having a housing and a substrate positionedwithin said housing in contacting engagement with said first and secondexhaust gases to convert said first and second exhaust gases intoprocessed exhaust gas; a third conduit in fluid communication with saidprocessed exhaust gas exiting from said catalyst; a first pre-sensor incontacting engagement with said first exhaust gas located upstream ofsaid substrate; a second pre-sensor in contacting engagement with saidsecond exhaust gas located upstream of said substrate; and a post-sensorin contacting engagement with said processed exhaust gas locateddownstream of said substrate.
 17. The marine engine exhaust system asrecited in claim 16, wherein said first and second conduits join to forma merged conduit upstream of said catalyst, and wherein said mergedconduit is in fluid communication between said first and second conduitsand said catalyst housing.
 18. The marine engine exhaust system asrecited in claim 17, wherein said merged conduit includes a pre-sensorin contacting engagement with said first and second exhaust gaseslocated upstream of said substrate.